Yeast Detection in Apple Juice Using Raman Spectroscopy

Abstract

Yeast (Saccharomyces cerevisiae spp.) causes unwanted fermentation in apple juiceproduction. Current methods for detecting yeast in the fermentation process are labor intensive andtime consuming, therefore, a rapid, reliable method is needed in order to assure consumers of a safeand high-quality product. Raman spectroscopy, an advanced optical technique based on lightscattering, was investigated as a rapid on-site detection method to provide a safety assessment ofyeasts contained in an apple juice droplet. In this study, a dispersive spectrophotometer system, witha 785-nm diode laser was employed. Chemometric methods such as Partial Least Squares (PLS)regression and classification analysis were used to evaluate low-concentration solutions of yeasts inapple juice drops smeared on glass plates. Apple juice samples containing yeast in variousconcentrations, and pure juice samples were analyzed to predict yeast detection thresholds. Truedetection of yeast varied between 83 and 100%. Good detection accuracy (97%) was obtained withyeasts concentrations of 100 CFU/ml and the best detection (100%) was achieved with aconcentration of 1 CFU/ml. The results obtained suggest that the Raman spectroscopy method mightbe used for rapid, accurate, on-line yeast detection in the apple juice industry.